A Prospective, Randomized, Masked, Placebo‐Controlled Multisite Clinical Study of Grapiprant, an EP4 Prostaglandin Receptor Antagonist (PRA), in Dogs with Osteoarthritis

Background This study evaluated the effectiveness and safety of grapiprant for treatment of pain in dogs with osteoarthritis (OA). Hypothesis/Objectives Grapiprant will relieve pain as measured by the owner's and veterinarian's evaluation of pain in dogs with OA. Another objective was evaluation of the safety of grapiprant. Animals Two hundred and eighty‐five client‐owned dogs with OA were enrolled and treated with grapiprant or placebo with 262 cases (N = 131 in each group) evaluable for the effectiveness analysis. Methods In this prospective, randomized, masked, placebo‐controlled study dogs were treated daily with grapiprant (2 mg/kg) per OS or placebo. Owners completed an evaluation using the Canine Brief Pain Inventory (CBPI) on days 0, 7, 14, 21, and 28. Success was defined as improvement in the CBPI. Veterinary assessments were made on screening and days 14 and 28. Safety was evaluated by physical examination, evaluation of clinical pathology results, and owner observations. Results Grapiprant treatment improved pain compared to placebo on day 28 (48.1 and 31.3% treatment successes respectively; P = .0315). The pain interference score (PIS) and pain severity score (PSS) improved in the grapiprant group compared to placebo (P = .0029 and 0.0022, respectively). Veterinary assessments were significantly better in the grapiprant‐treated dogs (P = .0086). Grapiprant generally was well tolerated, but a higher percentage of treated dogs (17.02%) had occasional vomiting as compared to the placebo group (6.25%). Conclusions and Clinical Importance Grapiprant is an effective treatment for alleviation of pain in dogs with OA, and represents a modality of treatment that may be better tolerated than current options.